I'd say that it all depends on your sound tastes. I'd think that the MMP should provide a little fatter bottom end, which seems like it might compliment your MBHO's nicely. The V2, I'd think would accentuate what the MBHO's already do well, which is crystal clean high end, so not sure if that would be too much. Based on my own personal tastes, I'd personally choose the MMP as a first choice to go with your MBHO's. I can't really comment on the OCM 661 since I've never owned one.